Flexible soft polyurethane foams are used on a large scale in the upholstered furniture and automobile industries. For the different applications and the different qualities needed for these purposes, it is necessary to be able to vary over a wide range the apparent density as well as, primarily, the hardness.
Inert inorganic or organic fillers have already been used in order to produce foams with a higher hardness. The hardness can also be increased by using so-called grafted polyols, which are synthesized by polymerization reactions of unsaturated monomers or by addition reactions in the polyols used for the foaming.
A lowering of the hardness is achieved by also using physical blowing agents, such as chlorofluorocarbons or methylene chloride. Lowering the hardness by these means is in contradiction with the endeavor, for environmental reasons, to restrict the use of chlorofluorocarbons as much as possible. The same is true for methylene chloride, which is physiologically not entirely safe.
To a certain extent, this applies also to the remaining physical blowing agents, the emission of which is severely restricted in many countries.
The apparent density of flexible polyurethane foams generally is between 14 and 50 kg/m.sup.3. Typical values for the hardness (DIN 53577) (at 40% compression) are between 1.0 and 6.0 kPa. If the amount of blowing agents used for the foaming is reduced, foams result with a comparatively higher density and hardness. This increase in density can be counteracted by increasing the amount of water added. The hardness, however, is unaffected by the addition of water and remains at the undesirably high level.
The present invention sets out to solve the technical problem of finding a method, which, with a reduced amount of physical blowing agent, particularly of chlorofluorocarbons or methylene chloride, and optionally with a tolerable increase in the amount of water added, enables flexible polyurethane foams to be produced with a hardness which is low relative to the resulting apparent density, (also referred to as weight by unit volume).
From EP-A-0 358 282, it is known that the amount of chlorofluorocarbons to be used for a method of the initially described kind can be reduced if the foaming is carried out in the presence of 0.001 to 1 parts by weight, based on 100 parts by weight of the polyol, of one or more water-soluble, organic polyelectrolytes, which are not cross linked and have a molecular weight of 1,000 to 20,000,000. Preferably, alkali salts of polyacrylates with a molecular weight of 2,000 to 10,000 should be used as polyelectrolytes in amounts of 0.1 to 0.5 parts by weight per 100 parts by weight of polyol.
A product is also already available under the name of ORTEGOL 300, which enables physical blowing agents, such as chlorofluorocarbons, to be partially replaced during polyurethane foaming. The product is a mixture of different active ingredients and has a pH of more than 12. At times, this procedure results in corrosion problems during storage and application. Moreover, there is a tendency for the individual components to separate.